A study from the Perelman School of Medicine at the University of Pennsylvania has found that people who work in jobs that are more physically demanding tend to be either shorter sleepers (fewer than 6 hours a night) or longer sleepers (longer than 9 hours). Since previous research has shown that people who report short or long sleep are more likely to have worse health over time, such as weight gain, heart disease and diabetes, the new study suggests that people's jobs may predispose them to unhealthy sleep patterns that could detrimentally affect their health. The findings go against the concept that physical activity in general seems to be healthy, and physical activity tends to be good for sleep.